Alignment-free solid laser apparatus

ABSTRACT

The alignment-free solid laser of the invention is characterized in that, an orientation prism having three inner surfaces perpendicular to one another, a bottom of equilateral triangle or circle shape, a corner apex located on the axis of the active material is located in front of one end of the active material and is used as a total reflective mirror of the resonant cavity, the other end of the active material is coated with a transitive-reflective film and is used as an output mirror, such that a laser resonant cavity is formed. This alignment-free solid laser has a simple structure, strong ability of misalignment-resistance, high stability, improved beam quality and reduced damage. Besides, it is easy to be operated and is easy to be standardized and modularized. It can be extensively used in military, industrial processing, medical and scientific research fields.

The subject application claims a priority under 35 U.S.C. §119 onChinese Patent Application No. 98113402.5, filed on Jan. 6, 1998, whichis herein incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to a solid laser, especially analignment-free solid laser suitable for industry, military (nationaldefence), medical and scientific research fields.

BACKGROUND OF THE INVENTION

At present, most widely used solid lasers consist of an active lasermaterial (also called laser rod), a pump system and an optical resonantcavity. After absorbing enough pump energy, the active material achievespopulation inversion and stimulated radiation is generated as a result.With the help of the optical cavity, the stimulated radiation oscillatesand is amplified in the cavity, and an amplified stimulated coherentlight beam, which is a laser beam of high intensity, is generated. Mostcavities consist of two mirrors parallel to each other and the activematerial is located on the axis of the cavity. The two plane mirrors arerequired to be parallel to each other exactly and are perpendicular tothe active material axis. When the angle between the two mirrors islarger than 20″ there will be no laser emission. Therefore, the lasermust be designed to have two sets of special means for its regulation tomeet the requirement for the cavity and needs to be regulated with thehelp of a special equipment, otherwise, the laser is impossible to beoperated normally. Thus, the structure and the regulation of the opticalresonant cavity of the laser have problems in installation, operationand maintenance. When the optical and cavity mirrors axes of the lasercavity deviate from their original position by an applied shock, hit orself-produced heat during the laser operation, the cavity can be indisalignment, even if it is regulated in alignment already. Oncedisalignment occurs, the output laser energy can be reduced, the beamquality can become inferior, and therefore the availability of the laseris affected. Even worse, the laser may have no output and becomeuseless. Besides, the inhomogeneity and the heat-induced distortion ofthe active material make the laser beam inferior and the local excessivepower density is likely to cause the damage of the laser material. Theseproblems are unavoidable for the conventional laser cavity, becauselaser beam must oscillates back and forth along the same path.Therefore, forming an alignment-free resonant cavity (i.e. getting laseroutput after installation without alignment.) to improve its machineryand heat stability and beam quality is an important problem demandingprompt solution. Prior solid lasers require high alignment accuracy andalignment is difficult in installation, furthermore, disalignment islikely to be occurred in bad conditions and is likely to be damagedunder high power, therefore, their availability is reduced.

In order to solve the above problems, a large amount of investigationshave been made both at home and abroad. A red sapphire laser cavityconsisted of a orientation prism and a plane output mirror was publishedin US Jemna Mechunika a optika No. 12 P.383-6 in 1968, while in patentU.S. Pat. No. 3,924,201, two right angle prisms (Paul prism) are used astwo total reflective mirrors of the resonant cavity, in between theactive material, Q-switch and an aside-output polarizer are located. Theabove two structures have partly solved the laser disalignment problemcaused by vibration, temperature variation and so on. However, they onlyhave the ability of avoiding misalignment and obtaining high stabilityin a special direction, while the installation and alignment are stilldifficult and they do not have the alignment-free characterisitics. A CNpatent CN 87.8.16562 has provided a stably aligned, linearly polarizedoutput laser, in which a corner prism is used as a reflector to form afolded optical resonant cavity. The total reflector and the outputmirror of the cavity are formed by a glass plate coated with films ofdifferent reflectance in different area. In the cavity an opticalalignment compensator is interpolated as an adjustable compensation forthe optical path deviation caused by machinery errors of opticalelements from optical axis. The optical resonant cavity can remain itsalignment and have low misalignment even under a great temperaturevariation condition. Therefore, the laser can output a stabilized,Q-switched and linearly polarized high power laser beam. Problems of thecavity are that it has low disalignment—resistance and is easy to bedeformed under high power condition. Besides, since the corner prism isused only as a reflector, the regulation of the optical alignmentcompensator is technologically complicated, and it is not analignment-free cavity. Now, the disalignment problem is usually solvedby using a module assembled by adhesion and then solidification. Howeverthis module must be calibrated and fixed. Besides, this technology iscomplicated, and can be used only once, because it is hard to berepaired.

DISCLOSURE OF THE INVENTION

The object of the present invention is to overcome the problem of theconventional lasers that the cavity must be regulated by two sets ofspecial means, and is to provide a simple structure, which can be stablyoperated after assemblage without alignment. This new structure hasstrong misalignment—resistance, therefore, can provide a stable outputlaser beam of small divergence angle under strong vibration and largetemperature variation environment.

The scheme of the present invention is as following:

The present invention provides an alignment-free solid laser, comprisingan active material, a resonant cavity, a pump lamp, a pump power and afocusing cavity, characterized in that the active material is located inthe focusing cavity, an orientation prism located in front of one end ofthe active material is used as a total reflector, the other end of theactive material is coated with a transitive—reflective film and is usedas a laser output mirror of the cavity, an applied voltage from the pumppower is applied to the two ends of the pump lamp, the pump light isreflected and focused on the active material by the inner surfaces ofthe focusing cavity, the corner apex of the mentioned orientation prismis located on the axis of the active material to form the resonantcavity, the three total reflective inner surfaces of the corner apex ofthe orientation prism are perpendicular to one another, the shape of theorientation prism is equivalent to a corner cut from a cube and itsbottom is of an equilateral triangle or circle shape;

The active material is an optical crystal which has been used in theconventional laser, such as red sapphire, Nd: glass, Nd: YAG, or thelike;

The active material located in the focusing cavity can be one or morerods. When it consists of two rods, one rod with a total reflective filmon one end and a transitive film on the other end is used as anoscillation rod, while the other rod with a transitive film on one endand a transitive-reflective film on the other end is used as anamplified rod. The two active material rods are symmetrically locatedrelatively to the axis passed through the orientation prism corner apexto form a series alignment-free solid laser;

When the active material consists of many rods, the active material rodarray is symmetrically distributed relatively to the axis passed throughthe corner apex of the orientation prism. One active material end closedto the orientation prism is coated with a transitive film, while theother end is coated with a transitive-reflective film and is used as anoutput mirror to form a high power solid laser with numbers of outputs,and without disalignment;

A Q-switch can also be put in the optical path between the activematerial end closed to the orientation prism and the orientation prism.

Comparing to the prior art, the present invention has the followingadvantages and effects:

1. The alignment-free solid laser according to the present inventionuses an orientation prism as a total reflector. It can also use, forexample, a Cr⁴⁺: YAG element as a Q-switch in the optical path, and usesone active material end with a transitive-reflective film as a outputmirror to form a laser cavity. This laser has strongdisalignment-resistance. The allowance of the disalignment angle of theorientation prism as a total reflector is up to ±20°, and the deviationof the prism central axis from the cavity axis is allowed up to D/4 (Dis the diameter of the active material). It is impossible for the priorlasers to achieve such results. The technology of the present inventionhas overcome the problem of the laser failure caused by the laser cavitydisalignment and therefore the laser can be operated normally afterassemblage without alignment;

2. The orientation prism or total reflector of this laser has a featureof parallel reflection in principle. It can overcome the problem of theoptical deformation caused by the refractance and gain nonhomogenity inthe laser medium, heat-induced deformation, heat-induced birefractanceetc. Therefore, the excellent performance of a uniform opticalfar-field, narrowed divergence angle and concentrated energy isachieved, and the laser beam quality is improved. The damage thresholdof the laser crystal and Q-switch device can be reduced and the problemof the laser damage of the solid laser is solved better when theorientation prism or total reflector is used in a continuous or highrepeated frequency Q-switched solid laser. Measurable distance, accuracyand angle resolution are increased when the orientation prism of totalreflector is used in laser distance-measuring instruments;

3. This laser has a simple structure, reliable performance and is easyto be assembled. It makes various related lasers modified easily, isalso of low cost. Furthermore, it is easy to be standardized andmodularized to form solid lasers with different specifications,different parameters and for different purposes, therefore, can beextensively used in military, industrial processing, medical andscientific research fields.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic drawing of the alignment-free solid laserstructure of the embodiment 1 of the present invention;

FIG. 2 is a side view of the orientation prism;

FIG. 3 is a schematic structure drawing of the orientation prism;

FIG. 4 is a schematic structure drawing of the series alignment-freesolid laser;

FIG. 5 and FIG. 6 are schematic structure drawings of two additionalalignment-free solid lasers;

FIG. 7 is a schematic structure drawing of the embodiment 2 of thepresent invention.

Wherein,

1—orientation prism

2—active material

3—focusing cavity

4—part reflector

5—pump lamp

6—pump power

7—cylindrical base

8—mounting nut

9—total reflector

2 a—active material

2 b—active material

0—corner apex

10—Q-switch.

Embodiments of the Invention

The present invention will be described further in conjunction withdrawings:

FIG. 1 is a schematic structure drawing of the alignment-free solidlaser of the embodiment 1 of the present invention. The active material2 is a red sapphire crystal. At its one end an orientation prism islocated. The corner apex of the orientation prism is located on the axisof the active material 2, the other end of the active material 2 iscoated with a transitive-reflective film and is used as the outputmirror 4. The pump system consists of the pump lamp 5, the pump power 6and the ellipsoidal cylindrical focusing cavity 3. An applied voltagefrom the pump power 6 is applied on the two ends of the pump lamp 5 tolight the lamp 5. The active material 2 and the pump lamp 5 are locatedrespectively on the two focused lines of the ellipsoidal cylindricalfocusing cavity 3 to ensure that the light beam from the pump lamp 5 isreflected by the inner surfaces of the ellipsoidal cylindrical focusingcavity 3 and is focused on the active material 2. Since the orientationprism 1 is located in front of one end of the active material 2 and itscorner apex is located on the axis of the active material 2, the laserbeam emitted from the active material 2 can be reflected back to thesame along the original path by the orientation prism 1 to oscillate andtherefore to achieve laser output. Besides, since one end of the activematerial 2 is coated with a transitive-reflective film and is used as apartly reflective reflector, the alignment-free performance of the lasercan be achieved after assemblage.

FIG. 7 is a schematic structure drawing of the embodiment 2 of thepresent invention, wherein, a Q-switch is added in the resonant cavityto improve the laser performance. The active material 2 is Nd³⁺: YAGcrystal. A saturable dye element can be used as the Q-switch 10 and theorientation prism 1 is located in front of one end of the activematerial 2. The corner apex 0 of the orientation prism 1 is located onthe axis of the active material 2, the other end of the active material2 is coated with a transitive-reflective film and is used as the laseroutput mirror 4. The pump lamp 5, which is connected to the pump power6, is located in the focusing cavity. The other structures of theembodiment are the same as the embodiment 1 and are unnecessary to bedescribed. The technological indexes are as followings:

Indexes of the low-frequency laser Active material Na³⁺: YAG Wavelength1.06 μm Repeat frequency 10-15 times/min Output energy ≧16 mj Angle ofdivergence ≦5 mrad Q-switch saturable dye element Disalignment allowanceof the resonant cavity mirror Translation D/4 (D is the diameter of theactive material) Rotation ±10°

The embodiment 3 is an alignment-free solid laser, in which Nd: YAGcrystal is used. Its structure is basically the same as the embodiment 2except that the Q-switch is a passitive one. The technological indexesare as followings:

Indexes of the high frequency laser: Active material Nd³⁺: YAGWavelength 1.06 μm Peak power 5 MW Repeat frequency 5˜20 pps Angle ofdivergence ≦5 mrad Q-switch Cr⁴⁺: YAG passitive Cooling mode liquidDisalignment allowance of the resonant cavity mirror: Translation D/4 (Dis the diameter of the active material) Rotation ±10°

FIG. 2 is a side view of the orientation prism. The operation principleis the following. At first, the light beam is incident into theorientation prism 1 from the bottom and is parallel to itself afterbeing reflected by the three surfaces of the orientation prism. Therotation of the orientation prism 1 about the corner apex 0 will notcause any change in the reflected beam direction. Next, the projectionsof the incident and reflected beams in the light direction is centrallysymmetrical about the corner apex 0 and the reflected beam is positivelyparallel to the incident beam as long as the light beam is reflectedsuccessively by the three right angle surfaces, regardless of the anglebetween the incident beam and the prism bottom. According to FIG. 3, inorder to ensure that the corner apex of the orientation prism 1 islocated on the axis of the active material 2, the orientation prism 1must be located on the axis of the cylindrical base 7. Then theorientation prism 1 and the cylindrical base 7 are tightly screwedtogether as a whole unit with screw nut 8.

FIG. 4 is a schematic structure drawing of a double-rod seriesembodiment, wherein the active material is Nd: glass crystal. Accordingto FIG. 4, the two active material 2 a and 2 b are symmetrically aboutthe corner apex of the orientation. One end of the active material 2 ais coated with a total reflective film and is used as the totalreflective mirror 9, while the other end A is coated with a transitivefilm and is used as the oscillation rod 2. One end of the second activematerial 2 b is coated with a transitive-reflective film and is used asthe partly reflective mirror 4, while the other end B with a transitivefilm is used as a amplifying rod 2 b to form a series alignment-freeresonant cavity. The laser beam from the oscillation rod 2 a, which isreflected into the active material 2 a by the reflective mirror 9, isthen coupled into the amplifying rod 2 b through the orientation prism1. It is incident onto the reflective mirror 4 to form oscillation andamplification, and finally, a laser beam is emitted from the partlyreflective mirror 4 of the amplifying rod 2 b.

FIGS. 5, 6 are schematic structure drawings of two additionalembodiments, wherein, the active material is Nd: YAG. In FIG. 5 theactive material is a hollow-cylinder, its end closed to the orientationprism is coated with a transitive film, while the other end is coatedwith a transitive-reflective film to form a alignment-free resonantcavity with the orientation prism 1 together. This laser has highfocusing efficiency and large mode volume, and therefore can meet therequirement for the output of high single-rod power and high beamquality. In FIG. 6, the active material array is symmetricallydistributed relatively to the axis passed through the corner apex 0. Theone end of the active material array is coated with a transitive film,while the other end is coated with a transitive-reflective film. The twoends and the orientation prism 1 form an alignment-free, array structurecavity that is suitable for the solid laser with multiple beams and highpower output.

What is claimed is:
 1. An alignment-free solid laser apparatuscomprising an active material having an axis, a first end coated with atransitive-reflective film, and a second end, an orientation prismhaving a bottom surface located close to the second end of the activematerial, a corner apex opposing the bottom surface and located on theaxis of the active material, and three inner surfaces being totalreflective surfaces and perpendicular to each other, a pump lampconnected to a pump power, and a focusing cavity reflecting and focusinglight from the pump lamp onto the active material, wherein the innersurfaces of the orientation prism form a resonant cavity for light fromthe active material, and light is emitted through the first end of theactive material that serves as an output mirror for the emission.
 2. Thealignment-free solid laser apparatus according to claim 1 wherein ashape of the orientation prism is equivalent to a corner cut from acube, and the bottom surface of the orientation prism is equilaterallytriangular or circular.
 3. The alignment-free solid laser apparatusaccording to claim 1 wherein the active material is a rod, and the axisof the active material is a longitudinal axis of the rod.
 4. Thealignment-free solid laser apparatus according to claim 1 wherein theactive material consists of a first rod and a second rod symmetricallylocated relative to the axis of the active material which passes throughthe corner apex of the orientation prism, and wherein a first end of thefirst rod is coated with a total reflective film and a second end of thefirst rod is coated with a transitive film, and a first end of thesecond rod is coated with a transitive-reflective film and a second endof the second rod is coated with a transitive film.
 5. Thealignment-free solid laser apparatus according to claim 1 wherein theactive material is an array of multiple rods which are symmetricallydistributed relatively to the axis of the active material which passesthrough the corner apex of the orientation prism, and the first ends ofthe rods next to the orientation prism are coated with transitive filmand the second ends of the rods are coated with transitive-reflectivefilm.
 6. The alignment-free solid laser apparatus according to claim 1further comprising a Q-switch between the second end of the activematerial and the bottom surface of the orientation prism.
 7. Analignment-free solid laser apparatus comprising an active materialhaving an axis, a first end coated with a transitive-reflective film,and a second end, an orientation prism having a bottom surface locatedclose to the second end of the active material, a corner apex opposingthe bottom surface and located substantially on the axis of the activematerial, and three inner surfaces being total reflective surfaces andperpendicular to each other, a pump lamp connected to a pump power, anda focusing cavity reflecting and focusing light from the pump lamp ontothe active material, wherein the inner surfaces of the orientation prismform a resonant cavity for light from the active material, and light isemitted through the first end of the active material that serves as anoutput mirror for the emission, and wherein the corner apex of theorientation prism on the axis of the active material renders the solidlaser apparatus substantially alignment free.
 8. The apparatus accordingto claim 7, wherein the corner apex of the orientation prism on the axisof the active material allows a misalignment angle of the orientationprism as a total reflector up to ±20° from the axis of the activematerial.
 9. The apparatus according to claim 7, wherein the corner apexof the orientation prism on the axis of the active material allows adeviation of a central axis of the orientation prism from the axis ofthe active material up to one fourth of a diameter of the activematerial.
 10. The apparatus according to claim 7, wherein a light beamenters into the orientation prism through the bottom surface and isreflected back by the three inner surfaces of the orientation prism suchthat the reflected light beam is in parallel to the entering beam. 11.The apparatus according to claim 10, wherein a rotation of theorientation prism about the corner apex does not cause a change in thedirection of the reflected beam.
 12. The apparatus according to claim10, wherein directions of the entering beam and reflected beam aresubstantially centrally symmetrical about the corner apex, and thereflected beam is positively parallel to the entering beam as long asthe entering beam is reflected successively by the three inner surfaces,regardless of an angle between the entering beam and the prism bottom.